充(chong)電(dian)電(dian)池(chi)(chi)已經(jing)成為當今電(dian)子產(chan)品的(de)一(yi)種標準電(dian)源，特(te)別(bie)是(shi)便(bian)攜設備：筆記本(ben)(ben)電(dian)腦(nao)、掌上導航儀、手機等(deng)(deng)。這(zhe)些產(chan)品需(xu)要消耗(hao)的(de)功率越來越大(da)，而可充(chong)電(dian)電(dian)池(chi)(chi)容(rong)量的(de)增(zeng)(zeng)長速(su)度(du)遠遠不能滿(man)足它們的(de)需(xu)求。功耗(hao)增(zeng)(zeng)長的(de)主要原因是(shi)設備功能的(de)增(zeng)(zeng)強(qiang)，例如(ru)：數碼相機與手機的(de)功能整合，筆記本(ben)(ben)電(dian)腦(nao)更高的(de)運算速(su)度(du)以及(ji)大(da)尺寸屏幕的(de)需(xu)求等(deng)(deng)等(deng)(deng)。便(bian)攜設備功耗(hao)的(de)增(zeng)(zeng)大(da)使得用可充(chong)電(dian)電(dian)池(chi)(chi)要比標準電(dian)池(chi)(chi)更便(bian)宜(yi)、更環(huan)保。

　　本文(wen)介紹了(le)(le)可充電(dian)(dian)電(dian)(dian)池(chi)的化學(xue)成分；同時說明了(le)(le)各種充電(dian)(dian)電(dian)(dian)池(chi)的典型(xing)(xing)特(te)征和選(xuan)擇(ze)電(dian)(dian)池(chi)類型(xing)(xing)時需要重點注意的事項(xiang)。另外還討論了(le)(le)在不使用(yong)微(wei)控制器或(huo)使用(yong)電(dian)(dian)源浪涌(yong)保護的主適(shi)配(pei)器的情(qing)況下如何構(gou)建單(dan)機結構(gou)，安全(quan)、快速(su)地(di)對鎳氫和鋰離子充電(dian)(dian)電(dian)(dian)池(chi)進行充電(dian)(dian)。

　　可充電電池類型

　　20世(shi)紀80年(nian)代(dai)的便攜設(she)備，如數(shu)字無繩電(dian)(dian)話(hua)、隨身聽和(he)電(dian)(dian)動剃須刀(dao)等，主要(yao)由鎳(nie)(nie)(nie)鎘(ge)(ge)(NiCd)電(dian)(dian)池(chi)(chi)供(gong)(gong)電(dian)(dian)。到了(le)90年(nian)代(dai)后(hou)期(qi)，鎳(nie)(nie)(nie)氫(NiMH)電(dian)(dian)池(chi)(chi)和(he)鋰離(li)(li)子(Li-Ion)電(dian)(dian)池(chi)(chi)逐漸(jian)進入市場并開(kai)始流行 因為價格比鎳(nie)(nie)(nie)氫和(he)鋰離(li)(li)子電(dian)(dian)池(chi)(chi)便宜(yi)，鎳(nie)(nie)(nie)鎘(ge)(ge)電(dian)(dian)池(chi)(chi)在低端應(ying)用(yong)中十分普遍。鎳(nie)(nie)(nie)鎘(ge)(ge)電(dian)(dian)池(chi)(chi)可提供(gong)(gong)最高的放電(dian)(dian)電(dian)(dian)流，適合短時間內(nei)需要(yao)大功率輸出(chu)的應(ying)用(yong)。

　　另一(yi)(yi)方面，鎳(nie)鎘(ge)電(dian)(dian)池(chi)曾經被所謂(wei)的(de)記(ji)憶效應(ying)困擾(現在(zai)的(de)鎳(nie)鎘(ge)電(dian)(dian)池(chi)很少考慮這個(ge)因素)，使電(dian)(dian)池(chi)容量降低。如果(guo)鎳(nie)鎘(ge)電(dian)(dian)池(chi)在(zai)未完全(quan)放(fang)電(dian)(dian)的(de)情況下再充電(dian)(dian)，一(yi)(yi)些活(huo)性物(wu)(wu)質會累積(ji)并且開始(shi)結(jie)晶(jing)(在(zai)陽(yang)極有100微(wei)米的(de)鎘(ge)累積(ji)層(ceng))，通過化學(xue)反應(ying)這層(ceng)物(wu)(wu)質會自(zi)行消失(一(yi)(yi)塊全(quan)新電(dian)(dian)池(chi)的(de)陽(yang)極大約(yue)有1微(wei)米厚度的(de)鎘(ge)結(jie)晶(jing))。

　　出現記憶效應會導致電池(chi)容量越來(lai)越小，端電壓(ya)越來(lai)越低，使(shi)得電池(chi)到達最低可用端電壓(ya)(關斷點(dian))的(de)(de)(de)時間比預(yu)期的(de)(de)(de)早許多，如(ru)圖(tu)1所(suo)示。鎳鎘(ge)(ge)電池(chi)的(de)(de)(de)另(ling)一個缺(que)點(dian)是它的(de)(de)(de)活性物(wu)質中含有有毒的(de)(de)(de)鎘(ge)(ge)。所(suo)以，歐洲法(fa)規2000/53/EG在(zai)2005年12月(yue)31號(hao)后(hou)禁止銷售鎳鎘(ge)(ge)充電電池(chi)。

　　鎳氫電池比鎳鎘電池更環保，但是價格更貴。鎳氫電池的放電電流略小，但受惰性效應的影響。惰性效應是比鎳鎘電池記憶效應稍輕的一種現象。惰性效應是由于鎳的結晶導致的。惰性效應和記憶效應一樣，導致無法完全使用可充電電池的全部容量，但都可以通過使用帶有放電功能的充電器來避免。

　　圖1. 鎳鎘電(dian)池的(de)(de)記憶效應與鎳氫電(dian)池的(de)(de)惰(duo)性(xing)效應之間的(de)(de)比(bi)較 鋰電(dian)子可(ke)充電(dian)電(dian)池價格最(zui)高，但具有(you)足夠(gou)高的(de)(de)能量密度，因(yin)而可(ke)以在(zai)給定尺寸下提供(gong)更(geng)優(you)性(xing)能，更(geng)適合小尺寸、高集成(cheng)度的(de)(de)便攜設備。

　　表1給出了各(ge)種類型電池的主要特性。

　　單(dan)機(ji)鎳氫電池快速充電器(qi)

　　雖(sui)然(ran)很(hen)多(duo)(duo)人更偏愛鋰離子電(dian)池，鎳(nie)氫電(dian)池的使(shi)用依然(ran)很(hen)流行(xing)。因(yin)為鎳(nie)氫電(dian)池比鋰離子電(dian)池便宜很(hen)多(duo)(duo)，所以在MP3播放器(qi)、閃(shan)光(guang)燈(deng)配件、車燈(deng)等設備(bei)中經常(chang)能看到標準的AA和AAA鎳(nie)氫電(dian)池。

　　一(yi)塊可充(chong)(chong)電(dian)(dian)(dian)鎳氫電(dian)(dian)(dian)池的(de)溫度(du)和(he)端電(dian)(dian)(dian)壓(ya)隨著(zhu)電(dian)(dian)(dian)池的(de)充(chong)(chong)電(dian)(dian)(dian)逐步上升(sheng)，在電(dian)(dian)(dian)池完全(quan)充(chong)(chong)滿后開始下降(圖2)。所以，鎳氫電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)器的(de)主要任(ren)務是檢測到這個突變點(dian)并中(zhong)斷充(chong)(chong)電(dian)(dian)(dian)，或(huo)者從快速充(chong)(chong)電(dian)(dian)(dian)切換(huan)到涓流充(chong)(chong)電(dian)(dian)(dian)。另(ling)外，在充(chong)(chong)電(dian)(dian)(dian)過程(cheng)中(zhong)對溫度(du)和(he)電(dian)(dian)(dian)壓(ya)進行(xing)連續監(jian)控可以提供(gong)系統的(de)安全(quan)性。

　　圖2. 這些曲(qu)線顯示(shi)了NiMH充(chong)電(dian)電(dian)池充(chong)電(dian)過程中典型的(de)電(dian)壓(頂部)和溫度(底部)隨時間的(de)變化 

　　DS2711/DS2712充(chong)(chong)(chong)(chong)電器(qi)(qi)具備上(shang)述功能(neng)。另外，它們可以單機工作(zuo)，不需要(yao)微(wei)控(kong)(kong)制器(qi)(qi)或微(wei)處理器(qi)(qi)監(jian)控(kong)(kong)。該系(xi)列產品是專門(men)為(wei)單節(jie)AA或AAA可充(chong)(chong)(chong)(chong)電電池(chi)(chi)設計的，同時也適用(yong)于(yu)(yu)串聯(lian)或并聯(lian)的兩節(jie)電池(chi)(chi)。DS2711采用(yong)線性控(kong)(kong)制結(jie)構，DS2712采用(yong)開關控(kong)(kong)制結(jie)構。為(wei)了最大限度地延(yan)長(chang)工作(zuo)時間、節(jie)約電池(chi)(chi)能(neng)量，這些(xie)充(chong)(chong)(chong)(chong)電器(qi)(qi)有4種充(chong)(chong)(chong)(chong)電模(mo)式：預(yu)充(chong)(chong)(chong)(chong)電、快速充(chong)(chong)(chong)(chong)電、浮(fu)充(chong)(chong)(chong)(chong)和涓流充(chong)(chong)(chong)(chong)電。在(zai)浮(fu)充(chong)(chong)(chong)(chong)模(mo)式下(xia)，電池(chi)(chi)充(chong)(chong)(chong)(chong)滿后充(chong)(chong)(chong)(chong)電速率被切(qie)換到一個比較(jiao)低的速率(對于(yu)(yu)DS2711而言是25%)。

　　除監控功(gong)能外(wai)，DS2711/DS2712充(chong)電(dian)(dian)(dian)器(qi)(qi)還帶有(you)內(nei)部計(ji)(ji)時(shi)器(qi)(qi)，通(tong)過(guo)連接到TMR引腳的(de)外(wai)部電(dian)(dian)(dian)阻設(she)定(ding)最(zui)大(da)充(chong)電(dian)(dian)(dian)時(shi)間(jian)(jian)，可(ke)將快(kuai)速充(chong)電(dian)(dian)(dian)時(shi)間(jian)(jian)設(she)置在0.5到10小(xiao)時(shi)。浮充(chong)時(shi)間(jian)(jian)已經設(she)定(ding)為最(zui)大(da)充(chong)電(dian)(dian)(dian)時(shi)間(jian)(jian)的(de)一半(0.25到5小(xiao)時(shi))。根據(ju)所要求的(de)充(chong)電(dian)(dian)(dian)時(shi)間(jian)(jian)(TAPPROX)，由下式計(ji)(ji)算電(dian)(dian)(dian)阻值(zhi)：

　　R = 1000TAPPROX / 1.5(Eq. 1)

　　快速充電模式下，如果超過最大充電時間，充電器會從快(kuai)速(su)充(chong)電模式(shi)(shi)切換(huan)到(dao)浮充(chong)模式(shi)(shi)，同時復位(wei)計時器。計時器開(kai)始為浮充(chong)過(guo)程(cheng)計時，如(ru)果達到(dao)預定(ding)的(de)浮充(chong)時間，充(chong)電器將從浮充(chong)模式(shi)(shi)切換(huan)到(dao)涓(juan)流模式(shi)(shi)(圖3)。

　　圖3. 該典型(xing)應用電路中，DS2711電池(chi)充電器

　　為2個(ge)串聯的 鎳(nie)氫充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian) VP1、VP2用于監視電(dian)(dian)(dian)(dian)壓，THM1、THM2配合熱(re)敏電(dian)(dian)(dian)(dian)阻(zu)用來(lai)監測電(dian)(dian)(dian)(dian)池(chi)的溫度。TMR (計(ji)時器(qi))和RSNS(檢(jian)流電(dian)(dian)(dian)(dian)阻(zu))用于設定充(chong)電(dian)(dian)(dian)(dian)時間和充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。DS2711/DS2712的另外(wai)一個(ge)特(te)性是可以檢(jian)測電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)故障(zhang)和堿性原電(dian)(dian)(dian)(dian)池(chi)。如果(guo)發生這些情況(kuang)，充(chong)電(dian)(dian)(dian)(dian)器(qi)會自(zi)行關機。

　　如何檢測(ce)堿(jian)性電池

　　全新的(de)(de)鎳氫AA電池的(de)(de)典型內(nei)阻(zu)在(zai)30mΩ到(dao)(dao)(dao)100mΩ，堿性(xing)電池的(de)(de)內(nei)阻(zu)一般在(zai)200mΩ到(dao)(dao)(dao)300mΩ (根據充(chong)電狀(zhuang)態，最(zui)高可到(dao)(dao)(dao)700mΩ)，出現故障的(de)(de)充(chong)電電池會有很高的(de)(de)內(nei)阻(zu)。DS2711/DS2712通過(guo)檢測到(dao)(dao)(dao)的(de)(de)電池電壓(VP1和VP2)和已設定的(de)(de)充(chong)電電流可以計算出待(dai)充(chong)電電池的(de)(de)內(nei)阻(zu)。

　　CTST引腳(用(yong)于(yu)電(dian)(dian)(dian)(dian)池(chi)(chi)測(ce)試、設置門限)控制(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)內阻(zu)(zu)的(de)(de)測(ce)量。VCTST是充電(dian)(dian)(dian)(dian)過程中的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)減去無充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流時的(de)(de)開路電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(OCV)后的(de)(de)差值。這個值等(deng)于(yu)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流乘以電(dian)(dian)(dian)(dian)池(chi)(chi)內阻(zu)(zu)的(de)(de)乘積。如(ru)果檢測(ce)引腳(VP1、VP2和VN1)與(yu)電(dian)(dian)(dian)(dian)池(chi)(chi)沒有采用(yong)Kelvin連接，引線電(dian)(dian)(dian)(dian)阻(zu)(zu)也將計(ji)入測(ce)量值，影響VCTST。計(ji)算外部電(dian)(dian)(dian)(dian)阻(zu)(zu)RCTST的(de)(de)公(gong)式為：

　　RCTST = 8000 [V2/A] / VCTST, 其中VCTST = ICharge * RCELL(Eq. 2)

　　例如，當以(yi)C/2速率(1.1A)為(wei)(wei)2200mAh NiMH電池充電時(shi)， 選擇RCELL = 150mΩ為(wei)(wei)電池內阻門(men)限時(shi), VCTST將(jiang)為(wei)(wei): VCTEST = ICHARGE * RCELL = 1.1A * 150mΩ = 0.165V 或: RCTST = 8000 [V2/A] / 0.165V = 48,485Ω

　　(最近的標準1%阻值為48.7kΩ) 如果超過VCTST門限(xian)(本例中(zhong)> 0.165V)，表明電池內阻高(gao)于(yu)150mΩ，芯片會提供邏(luo)輯指(zhi)示或出錯信(xin)息指(zhi)示(LED1、LED2)，同時(shi)停止(zhi)充電過程(圖(tu)4)。

　　圖4. 圖3中所示充電器的(de)充電流程

　　單機鋰(li)離子電池快速(su)充電器

　　因為不需要檢測電壓變化率(dV/dt)，鋰離子電池充電器比鎳氫電(dian)(dian)池簡(jian)單(dan)。同時，由于(yu)(yu)鋰離子電(dian)(dian)池對(dui)過充(chong)非常敏感，充(chong)電(dian)(dian)器需要一個精(jing)確的(de)4.2V ± 50mV電(dian)(dian)源保證恒功率充(chong)電(dian)(dian)。至于(yu)(yu)鎳氫電(dian)(dian)池，充(chong)電(dian)(dian)器不(bu)僅(jin)需要電(dian)(dian)壓監測，還需要其它監控功能(溫度、計(ji)時等)。

　　單機鋰離子電池充電器MAX8601內置所謂的Vbatt可控電壓源，它可以在+25°C提供4.2V ± 0.021V，或在40°C < T < 85°C提供4.2V ± 0.034V的精度。當通過Vbatt連接給鋰離子電池充電時，充電器可以保持恒定輸出功(gong)率(圖5)，外部(bu)(bu)電(dian)(dian)(dian)阻(zu)(接SETI引腳)和外部(bu)(bu)電(dian)(dian)(dian)容(rong)(接CT引腳)可以設(she)定充電(dian)(dian)(dian)電(dian)(dian)(dian)流和內(nei)部(bu)(bu)計時。該充電(dian)(dian)(dian)器(qi)還通過(guo)一個(ge)負(fu)溫度系數電(dian)(dian)(dian)阻(zu)來監控電(dian)(dian)(dian)池的溫度。

　　圖5. MAX8601鋰離子電(dian)(dian)池單(dan)機(ji)充電(dian)(dian)器(qi)的典(dian)型應用(yong)電(dian)(dian)路圖

　　MAX8601充電器(qi)的(de)主(zhu)要優點是可以(yi)通過外(wai)部適(shi)配(pei)器(qi)或USB端(duan)(duan)口(kou)給電池充電(圖6)。USB端(duan)(duan)口(kou)根(gen)據USEL引(yin)腳(jiao)的(de)設置可以(yi)提供100mA、500mA電流(典型(xing)USB輸出電流)。該芯(xin)片會(hui)自動選擇外(wai)部電源(yuan)(yuan)(主(zhu)適(shi)配(pei)器(qi)或USB)。如果兩(liang)個電源(yuan)(yuan)同(tong)時(shi)存在，它會(hui)選擇主(zhu)適(shi)配(pei)器(qi)進(jin)行(xing)充電。任何一個電源(yuan)(yuan)都必(bi)須能(neng)夠提供最小(xiao)4.5V的(de)電壓。

　　MAX8601具有低電池電壓預充、限壓/限流快速充電和浮充模式等控制算法，優化了鋰離子電池充電。器件還有上電(dian)復位以及電(dian)池過壓、高溫/低溫檢測(ce)和充電(dian)時間的連續監(jian)測(ce)功(gong)能。

　　圖(tu)6. 圖(tu)5中充電器的充電流程圖(tu)

　 DS2711/DS2712和MAX8601都是單機充電器，它們具有多種監控(kong)(kong)功能(電(dian)壓、電(dian)流、溫度、計(ji)時(shi)等)，既不(bu)需要(yao)微控(kong)(kong)制器(qi)監控(kong)(kong)，也不(bu)需要(yao)電(dian)源浪涌保護，而且提供清(qing)晰、簡單的外部切(qie)換。